Incidents in the recent year, in which children watching a television program of animated cartoon had suffered a seizure, has lead the broadcasting industry to set a guideline for video images to be broadcasted, and to place great importance on technique pertaining to detection and conversion of a video scene that may cause an adverse effect to human beings. It has been pointed out specifically that video images, in which a bright image having a duration of three vertical scanning and a dark image having a duration of three vertical scanning are displayed repeatedly, may cause an adverse effect mentally and/or physically to the viewers.
A video signal character detecting device for detecting a video scene based on presence or absence of a synchronizing signal has been known heretofore such as one disclosed in Japanese Patent Laid-Open Publication No. H06-233235, in order to avoid recording of signals that need not be recorded in apparatuses such as video recorders.
FIG. 7 shows a block diagram of a video signal character detecting device of the prior art. In FIG. 7, a synchronization detector 201 detects the presence or absence of a synchronizing signal. A microcomputer 202 suspends a recording operation of the video recorder when an unnecessary signal is detected. A signal separation circuit 203 separates a video signal from an input signal. A synchronizing signal separation circuit 204 separates a synchronizing signal contained in the video signal. A first differential circuit 205 differentiates the synchronizing signal. A second differential circuit 206 differentiates the video signal and the synchronizing signal. A subtraction circuit 207 generates a subtraction signal between the two differential signals. The subtraction signal corresponds to a differential signal of a video signal without a synchronizing signal.
The video signal character detecting device constructed as above operates in a manner, which will be described below.
First, the subtraction circuit 207 outputs the subtraction signal to the microcomputer 202. If the subtraction signal does not exceed a predetermined threshold, the microcomputer 202 determines the input signal as an unnecessary signal, and suspends a recording operation of the video recorder.
The foregoing structure has a problem, however, that it is unable to detect video scenes, which may cause an adverse effect to viewers, such as a scene, in which light and darkness are repeated periodically on an entire screen, or a scene, in which red and blue are repeated periodically.